The present invention relates to magnet wire insulation designed to withstand voltages present in inverter driven motors for a sustained period of time. More specifically, the present invention relates to magnet wire insulation that is intended to improve the life of motor windings when used in conjunction with an inverter drive, e.g., pulse-width modulated variable frequency drive.
Inverter drives and inverter driven motors have received increased attention because of continuing needs for greater energy efficiency. It has been estimated that three-phase induction motors consume 60-70% of the electrical energy used in the United States. These motors obviously waste substantial energy when run at full speed when conditions do not require it.
An adjustable speed drive (ASD) allows a motor to operate at variable speed by providing variable frequency to the motor. Electronic ASDs convert the incoming line voltage at 60 Hz to direct current (DC). The inverter then generates variable frequencies as input to the motor. These variable frequencies, however, can exhibit steep wave shapes that have been linked to premature motor winding failures in 440+voltage motors. The mode of failure in these motor windings has been linked to the degradation of the wire insulation caused by the high voltage and higher frequency wave shapes.
Various attempts have been made to reduce premature failures as a result of degradation of the wire insulation. These attempts have included minimizing damage to the wire and insulation during handling and manufacture of the motors, and using shorter lead lengths from the inverter to the motor where appropriate. Further, a reactor coil or a filter between the inverter and the motor can extend the life of the windings by reducing the voltage spikes and high frequencies generated by the inverter cable/motor combination. However, such coils are expensive and add to the overall cost of the system. Increasing the amount of insulation from standard heavy build magnet wire can improve the life of the windings in the motor, but this option is both expensive and decreases the amount of space for the copper in the motor, thereby producing a less efficient motor. Another option includes increasing the amount of varnish in the motor windings, however, this strategy is ineffective if the windings are not completely covered.
Therefore, there is a need for a magnet wire insulation that is designed to withstand voltages which are present in inverter driven motors for longer periods of time as compared to the present constructions.